The present invention relates to the proper positioning and orienting of work pieces at a work station of any appropriate operation requiring precise positioning of the work piece. Examples include machining, inspection, balancing, and assembly operations. For purposes of an exemplary showing the invention will be described in terms of a machining operation in a machining center or the like, where machine operations are performed on the work piece. That the work piece be properly positioned and oriented to receive the machining operation is, of course, imperative. It is well known that properly positioning, orienting and securing the work piece at a work station in many instances can take far longer than the machining operation, itself. Prior art workers have devised many means for accomplishing this task. Of particular note is the development of work holding means comprising a receiver and a carrier or pallet. The receiver is mounted on an appropriate surface, either located at the work station of the machining center, or shiftable to such a position. The work piece upon which one or more machining operations are to be performed is affixed to the pallet. The pallet, carrying the work piece, is properly mounted on the receiver and is firmly clamped thereto.
The mating of and clamping of the work piece carrying pallet to the receiver is intended to assure proper positioning and orientation of the work piece at the work station. U.S. Pat. Nos. 4,575,062 and 4,643,410 illustrate work holding systems of this general type, which have been in use for many years. For purposes of explanation, let it be assumed that the surface to which the receiver is attached is a horizontal surface. The receiver and the pallet are provided with circular rings having abuttable horizontal surfaces provided with radially oriented teeth. The teeth of the pallet and receiver rings interengage. Interengagement of these radial teeth on the pallet and receiver rings enables achievement of precise concentricity or centering of the pallet with respect to the receiver. Means are also provided so that the pallet is properly horizontally seated with respect to the receiver, often referred to as "flatness" or "parallelism" of the pallet with respect to the receiver. This assumes that the axis of the pallet is vertical. This causes the centered vertical axes of the receiver and pallet to be coaxial. The interengaged teeth of the toothed rings of the pallet and receiver provided means for properly orienting the work piece about the axis of the receiver (frequently called clocking). These factors result in the precise and proper repeatable positioning of the work piece at the work station of the machining center. The degree of repeatable precision achieved is limited by the degree of precision with which the interengaging teeth can be formed.
The present invention is based upon the discovery that a work holding system comprising a pallet and a receiver can be provided which can achieve a degree of repeatable precision with respect to concentricity or centering, flatness or parallelism, and clocking, hitherto unobtainable. For example, clocking can be repeatably achieved within about one arc second. Flatness or parallelism can be repeatably achieved within about 0.0001 inch. Concentricity or centering can be repeatably achieved within about 0.0002 inch. The pallet and receiver incorporate cooperating male and female polygons and cooperating annular abutment surfaces.
The pallet and receiver of the work holder system of the present invention can be of relatively simple construction. Any appropriate means can be used to clamp the pallet to the receiver.